Vapor electric device



July 17, 1928.

L. T. ROBINSON ET AL VAPOR ELECTRIC DEVIC E Filed Nov. 19, 1925 mm v\vRA. b

Q K M m eC e w 0 VVT z b Patented July 17, 1928.

- UNITED STATES 1,677,689 PATENT OFFICE.

LEWIS '.l'.. ROBINSON AND CAMILLE A. SABBAH, OI BCHENEC'I'ADY, NEW YORK,A8-

BIGNOBS '10 GENERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORK.

VAEOR ELECTRIC DEVICE.

Application filed November 18, 1925. Serial llo. 70,201.

Our invention relates to vapor electric devices wherein current istransmitted between a cathode and an anode alternately charged topositive and ne ative polarities, and has for its principal ject theprovlsion of a method and means for preventing the transmission ofinverse current throug the anode when it is charged to a negativepotential.

In the operation of vapor electric devices,

such as the mercury rectifier, current is transmitted between apositively charged anode and the cathode through an electric are whichcarries a multitude of positive ions. The presence of positive ions inthe vicinity of the anode is desirable when it is positively charged andis transmitting current because these ions reduce space charge andfacilitate the transmission of current through the device. When theanode is charged to a negative polarity and is not transmitting current,however, thepresence of positive ions in the vicinity of the anode isundesirable for the reason that they are attracted to the anode and tendto raise its temperature to a point at which electrons are emitted.These electrons ionize the surrounding vapor, thus producing morepositiveions and establishing a condition likely to lead to theformation of destructive arcs, commonly denoted by the expression areback, between the negatively charged anode and some other part of thedevice.

It is customary to surround the anodes of a vapor electric device with ashield or baffle for protecting them from the positive ions of the arewhen they are not trans.

mitting current. With this construction, trouble is encountered due tothe presence of positive ions within the anode shield or baflie at theinstant the anode polarity is changed from a positive to a negativevalue. In accordance with our invention, this difiiculty is avoided bythe provision of means for attracting the positive ions away from thenegatively charged anode and for intercepting the electrons emitted fromthe anode before they have had an appreciable efiect on the surroundingvapor.

Our invention will be better understood from the following descriptionwhen considered in connection with the accompanyingdrawings and itsscope will be pointed out in the appended claims. 1

Referring to the drawings, Fig. 1 shows a fragmentary sectional view ofa mercury rectifier wherein my invention has been embodled' Frgs. 2 and3 show various details thereof F1g. 4is a sector diagram showing thephase relation between the anode, shield and control electrode voltages;and Figs. 5 and 6 relate to a modified form of mercury rectifier.

Figs. 1, 2 and 3 show a mercury rectifier wherein current from asuitable source is transmltted through an are between an anode 1 and acathode 2 which is located 1n a container 3 and is supported by aninsulated wall portion 4 of this container. Chambers 5 and 6 areprovided for circulatmg a cooling medium in contact with the containerwalls. It will be observed that an insulation member 7 is arranged toform a seal between the anode 1 and the cover of the container 3 uponwhich it is supported that a control electrode 8 and an anode shield 9are supported by an insulator 10 extending between the anode and thetank cover, that a p1pe 11 is provided for applying a coolm medium tothe anode 1, that the anode 1 is connected to a lead 12 through aprimary winding 13 of an induction device comprising an adjustable coremember 15 and a secondary winding 16, that control electrode 8 isconnected to the anode 1 through a resistor 17 and the secondary winding16, and that the shield 9 is insulated from the control electrode 8 byinsulation member'IO and is connected to the control electrode 8 throughan adjustable condenser 18 which is connected to the .s'ec= ondarycircuit 16 in series with a resistor 19. It will be readily understoodthat, while onl one anode appears in the figure, the recti er willusually comprise either a palr of electrodes connected to the oppositeterminals of a single phase source or a plurality of anodes connected toa polyphase source in any suitable manner.

With the connections illustrated, the phase relation between thevoltages of the anode 1 and the control electrode 8 is dependent on theadjustment of the movable core member 15 of reactance device 14, and thephase relation between the voltages of control electrode 8 and shield 9is determined by adjustment of condenser 18. Assuming the vectors 1', 8'and 9' of Fig. 4 to represent the voltages of anode 1, control electrode8 and shield 9 respectively, it will be seen that the control electrodevoltage leads both the anode and shield voltages and is somewhat largerthan the anode voltage due to the fact that it is connected to the anodethrou h the secondary winding 16 which raises t e control electrodevoltage above that of the anode by an amount dependent on the mag-'nitude of the current transmitted through the anode.

The manner in which the phase relation between the anode, controlelectrode and shield voltages is utilized to prevent are back due to theresence of positive ions within the shield when the anode assumes anegative polarity will be explained on the assumption that transmissionof current between the anode and cathode has ceased and the anode hasjust assumed a negative polarity. Under these conditions, the shield ischarged to a negative value somewhat greater than that of the anode, thepolarity of the control electrode is still positive and the positiveions are largely prevented from reaching the anode both due to thepositively charged control electrode which repels them and to thecomparatively large negatively charged surface of the shield whichattracts them. Are back due to the residual positive ions is thusprevented.

As previously indicated, are back is also likely to be produced by theionization of the surrounding vapor due to the emission of electronsfrom the negatively charged anode. This difiiculty is most ronouncedwhen the anode is operated at a igh temperature and is charged to acomparatively high negative voltage. Referring to the vector diagram ofFig. 4, it will be noted that the control electrode assumes a negativepotential soon after the polarity of the anode is changed from a ositiveto a negative. The interval of time etween the changes in the polaritiesof the anode and control electrode may be controlled by the inductancedevice 14 and should be just suflicient to allow deionization of thevapor within the shield. With proper adjustment of the reactance device14, a negative voltage is applied to the control electrode while thenegative voltage of the anode is comparatively small and the emission ofelectrons from the anode is retarded in a manner to prevent ionizationand are back. The control electrode thus performs the double function ofprotecting the anode from the positive ions during deionization and ofpreventing ionization of the vapor by electrons emitted from the anodewhen it is charged to a comparatively high negativevoltage.

Fig. 5 is a diagrammatic showing of a system wherein current suppliedfrom a suitable alternating current source is transmitted to a directcurrent circuit 20 through a polyphase transformer 21 comprisingsecondary windings 22, 23 and 24. a rectifier comprising anode 25 andcathode 26, an interphase transformer 27 of well known construction, anda reactor 28 which is provided for smoothin out pulsations in thecurrent of the circu1t20. It will of course be understood that, whileonly one anode 25 has been illustrated, the rectifier will comprise alurality of anodes each connected to a di erent secondary terminal ofthe transformer. A spiral grid or control electrode 32 is interposedbetween the anode 25 and cathode 26 and is connected to the anodethrough the resistor 17 and a phase control device 28 supplied withcurrent from the left hand part of the secondary winding 22 through aotential transformer 29. As indicated by Fig, 6, the active surface ofthe anode 25 is located within a funnel-shaped bafile to which it isconnected through a resistor 31. The resistor 31 corresponds to theresistor 19 of Fig. 1 and may be connected between the anode and shieldeither independently of the phase control device or in series therewithas previously explained.

The form of anode shield illustrated by Fig. 6 has the advantage that itradiates heat away from the anode to the cool wall of the container andallows the vapor surrounding the anode to readily expand toward thecontainer wall thus preventing excessive rise in temperature and vaor-pressure around the anode. The operation of the modification shown byFigs 5 and 6 will be apparent in vieZv of the previous discussion ofFigs. 1 to The embodiments of the invention illustrated and describedherein have been selected for the purpose of clearly setting forth theprinciples involved. It will be apparent;

however, that the invention is susceptible 0 being modified to meet thedifferent conditions encountered in its use and we therefore aim tocover by the appended claims all modifications within the true spiritand scope of our invention.

What we claim as new and desire to secure by Letters Patent of theUnited States, 1s.:-- 1. The method of operating a vapor electric devicecomprising a control electrode inter osed between an anode and an anodeshiel which comprises changing the polarity of said shield and anode,and thereafter changing the polarity of said control electrode.

2. The method of operating a vapor electric device comprising a controlelectrode interposed between an anode and an anode shield, whichcomprises successively changit is charged. to a negative polarity, acontrol electrode interposed between said shield and anode, means forapplying voltages to said shield and control electrode, and means forcontrolling the relation between the voltage of said anode and thevoltages of said shield and control electrode.

4. A vapor electric device wherein current is transmitted through an arebetween a cathode and an anode alternately charged to positive andnegative polarities, comprising an arc shield for protecting said anodewhen it is charged to a negative polarity, a control electrodeinterposed between said shield and anode, means for applying voltages tosaid shield and control electrode, and means for controlling the phaserelation between the voltages of said shield and control electrode.

5. A vapor electric device comprising an external anode, an anode shieldinsulated from said anode, and a control electrode interposed betweensaid anode and shield and insulated therefrom.

6. A vapor electric device comprising an external anode, an anode shieldinsulated from said anode, a control electrode interposed between saidanode and shield and insulated therefrom, and means for applying acooling medium to the external surface of said anode.

A vapor electric device comprising an external anode, an anode shieldinsulated from said anode, a control electrode interposed between saidanode and shield and insulated therefrom, and means for applyingpotentials of predetermined magnitude and phase relation to said anode,control electrode and shield.

8. The method of operating a vapor elec-'.

during deionization of the vapor enclosed within said shield.

9. The method of operating a vapor electric device comprising acontrol-electrode interposed between an anode and an anode sh eld, whichcomprises applying a negative potential to said anode, applying apositive potential at said control electrode during deionization 01 thevapor within said shield, and changing the polarity of said controlelectrode at a predetermined time after said anode has been charged to anegative poten: tial.

In witness whereof, we have hereunto set our hands.

LEWIS T. ROBINSON. CAMILLE A. SABBAH.

